1. Field of the Invention
The present invention relates to an image display apparatus which typically includes a liquid crystal display element, an organic electro luminescence element, etc., and to an image processing circuit applied to such image display apparatus. In particular, the invention relates to an image processing circuit and an image display apparatus to which an image quality improvement technology is applied.
2. Description of the Related Art
An image display apparatus such as a liquid crystal display element, an organic electro luminescence element, etc. adopts arts of whiteout prevention and white level expansion, etc. for improving image quality. Whiteout prevention is an art of preventing the detail of an image from being lost in highlight area, which is attained by detecting the maximum luminance of luminance signals and if the luminance level is saturated, reducing the luminance intensity with gamma correction. The white level expansion is an art of improving the contrast expression in high luminance portion by obtaining a luminance distribution within the display image from image signals, and when the area of a bright pixel portion, having the luminance level close to but under 100 percent of the maximum level, exceeds a given area threshold, carrying out gamma correction so as to further increase the area's luminance level up to 100 percent. Such approach has been applied to the whole portion of a display image uniformly in the past.
Japanese Patent Application Publication No. H11-113019 discloses an image display apparatus in which a white balance adjustment and gamma correction that is peculiar to a localized portion within a display image and different from the other portion thereof is applied to the localized portion. According to the disclosure, occurrence of luminance irregularity, chromaticity unevenness, etc. within the display image due to production tolerance of liquid crystal display elements and luminous energy distribution of back lights and so on, is prevented.